Various personal authentication methods which use biometric information of an iris, fingerprint, face, etc., have been proposed. In recent years, a personal authentication technique utilizing iris recognition has been started to be used for entrance/exit management in a restricted building, bank ATMs (Automated Teller Machines), PC login applications, etc.
Personal authentication using an iris is for example implemented by the following steps (see Japanese Unexamined PCT National Phase Publication No. 8-504979 (hereinafter, referred to as Document 1)):                1. Irradiate an iris using near-infrared LED, or the like, to obtain an iris image;        2. Detect the pupil/iris border and iris/sclera (white portion) border to extract an iris region;        3. Transform pixel coordinate values of the iris region from rectangular coordinates to polar coordinates;        4 Gabor-transform the brightness of the coordinate-transformed iris region;        5. Binarize the real part and imaginary part of the output of the Gabor transform to generate an iris code;        6. Generate an iris code for a registrant through above steps 1 to 5 to register the iris code in a registration database; and        7 Generate an iris code for a person who is to be authenticated through above steps 1 to 5 and compare the generated iris code with the iris code in the registration database to determine, based on differences between the iris codes, whether or not he/she is a person who has been registered in the registration database.        
Near-infrared light is used for irradiation at step 1 because it is not perceived by a human eye, and therefore, a person who is to be authenticated does not feel glare. Almost all the people on the earth have brown irises (some races have blue or gray irises, but they are minorities in the world), and the iris pattern of brown irises can be captured with high contrast under near-infrared light although it is difficult to visually identify the iris patter of brown irises under visible light. It should be noted that the iris pattern of blue or gray irises can also be captured under near-infrared light.